TM 10-3930-664-10 b. Indicators. KEY CONTROL OR INDICATOR FUNCTION 1 Parking Brake Indicator Light Amber  indicator  illuminates  when  the  ignition  switch  is  ON  and  the  parking brake is engaged. 2 Differential Lock Indicator Light Amber indicator illuminates when the ignition switch is ON and the differential lock is engaged. CAUTION 3 Low Engine Oil Pressure Indicator Red  indicator  illuminates  whenever  the  engine  oil  pressure  drops  below  15 psi (103 kPa). 4 Lateral Level Indicator Visually indicates, by position of ball in vial the attitude of the 4KRTFL when operating on a right or left sideslope. Stop the engine whenever the low engine oil pressure indicator is illuminated.  Do not operate the engine at oil pressures lower than 15 psi (103 kPa). 2-4